page.html.twig default regions

Question

I'm creating a custom theme with base theme: stable. I have copied the template/layout/page.html.twig file into my theme. As I am reading the twig file I have noticed that there are some regions that I am not providing but are still being rendered.

Part of the file comment lists the regions available.

/*
 * Regions:
 * - page.header: Items for the header region.
 * - page.primary_menu: Items for the primary menu region.
 * - page.secondary_menu: Items for the secondary menu region.
 * - page.highlighted: Items for the highlighted content region.
 * - page.help: Dynamic help text, mostly for admin pages.
 * - page.content: The main content of the current page.
 * - page.sidebar_first: Items for the first sidebar.
 * - page.sidebar_second: Items for the second sidebar.
 * - page.footer: Items for the footer region.
 * - page.breadcrumb: Items for the breadcrumb region.
 */

I went looking in the stable.info.yml file and noticed there is not an entry for regions: so I am at a loss as how the page.html.twig file is able to render regions that are not listed in the stable.info.yml file.

Questions

• How does this work without being defined in the stable.info.yml file.
• Are there any other regions that work like this that are not in the page.html.twig file.

Answer 1

If no regions are specified in the theme, the core provides defaults itself.

From the docs page: https://www.drupal.org/docs/8/theming-drupal-8/adding-regions-to-a-theme

Default Regions:

page.header: Items for the header region.

page.primary_menu: Items for the primary menu region.

page.secondary_menu: Items for the secondary menu region.

page.highlighted: Items for the highlighted content region.

page.help: Dynamic help text, mostly for admin pages.

page.content: The main content of the current page.

page.sidebar_first: Items for the first sidebar.

page.sidebar_second: Items for the second sidebar.

page.footer: Items for the footer region.

page.breadcrumb: Items for the breadcrumb region.

If your theme does not declare any regions Drupal will assume this set of defaults. These regions correspond with what the default core/modules/system/templates/page.html.twig file expects, as well as two hidden regions, page_top, and page_bottom - you don't need to declare these final two if you override the defaults, however the {{ page_top }} and {{ page_bottom }} Twig variables should be retained in the html.html.twig template.

Answer 2

After some more research I finally found it here. The following is a quote of the section explaining how it works.

Default Regions

See the page.html.twig documentation for a list of default regions.

1. page.header
2. page.primary_menu
3. page.secondary_menu
4. page.highlighted
5. page.help (dynamic help text, mostly for admin pages)
6. page.content (main content of current page)
7. page.sidebar_first
8. page.sidebar_second
9. page.footer
10. page.breadcrumb

If your theme does not declare any regions Drupal will assume this set of defaults. These regions correspond with what the default core/modules/system/templates/page.html.twig file expects, as well as two hidden regions, page_top, and page_bottom - you don't need to declare these final two if you override the defaults, however the {{ page_top }} and {{ page_bottom }} Twig variables should be retained in the html.html.twig template.